Influence of Palaeoenvironmental Changes on the Formation of the Vilku Bog Deposits

Models of peat accumulation assume that peat decomposition occurs mostly above the water table, with little or no decomposition once peat enters the deeper, saturated, anoxic zone. However, few such measurements of peat decomposition exist. In this paper we quantified differences in degree of decomposition, botanical composition, and organic chemical composition of peat from three temperate peatlands with different water table levels. All sites had a thick layer of herbaceous peat, capped by a layer of Sphagnum peat. The lignin content and degree of decomposition, measured by the pyrophosphate index, generally increased with depth. Analysis of the lignin with cupric oxide (CuO) oxidation revealed most of the chemical differences between peat deposits occurred in the upper, aerated peat layer, as expected. The upper layer of Sphagnum peat was characterized by high p-hydroxyl phenolic yield, whereas Sphagnum peat below the water table exhibited a high degree of humification and high yield of vanillyl oxidation products despite being of similar botanical composition. Surprisingly, herbaceous peat below the water table was similar in terms of degree of decomposition to younger herbaceous peat. The results confirm that peat decomposition occurs mostly above the water table, although botanical source, climate, and local hydrology interact to create multiple trajectories in peat chemistry.

Mires are known as consistent environmental archives, but humic acids are the fraction of peat that is most recalcitrant and refractory to organic matter degradation, thus data on environmental changes during mire development can be recorded into them. This work was focused on the studies of stable isotopic ratios delta carbon-13 and delta nitrogen-15, and their distribution in humic acids within fen peat layers of different depths and peat composition. The variations in delta carbon-13 reflect isotopic variations in peat-forming plants over time and can be considered as a function of photosynthetic pathway that is being used to fix carbon dioxide. At the same time, variations in delta nitrogen-15 show nitrogen fixation in peat-forming plants and can be traced along with peat decomposition degree and depth. Properties of humic acids were studied in 2018 at 3 fens located in Latvia and Southern Finland, and comparatively they show properties. The method used for the determination of stable isotopes was the isotope-ratio mass spectrometry that was performed in the Faculty of Chemistry, University of Latvia. Results on delta carbon-13 indicate signal of C3 peat-forming plants, while signal of C4 peat-forming plants is not evident, which can be explained by non-efficient carbon dioxide fixation in fen vegetation. Results on delta nitrogen-15 show variations in nitrogen fixation in fen vegetation. Data show nitrogen fixation in terrestrial plants, however significant shifts in absolute isotope values indicate dependence on variations in peat decomposition degree and botanical composition. Data suggest that differences in peat botanical composition, decomposition degree and site dependent characteristics reflect in differences in delta carbon-13 and delta nitrogen-15 variations

В статье представлены результаты определения группового химического состава органического вещества распространенных видов торфа среднетаежной зоны Западной Сибири. Выявлены различия группового химического состава органического вещества торфа в зависимости от ботанического состава и степени разложения. Полученные данные сопоставлены с данными, характеризующими групповой химический состав органического вещества разных видов торфа южнотаежной зоны Западной Сибири. Дано описание физико-географических характеристик и ландшафтных особенностей болотного массива «Мухрино».

The aims of this study are to investigate historical PAH deposition through the analysis of PAHs in bulk peat cores and reveal the different distribution of PAHs in Sphagnum and Ledum peat from peat cores. Peat cores from Jingjiang peatland are collected, and Sphagnum peat samples are manually separated from bulk peat. The remaining bulk peat samples are defined as “Ledum peat.” 137Cs is used to date the peat cores. PAH contents as well as physicochemical property of Sphagnum and Ledum peat are determined. The PAH deposition rates measured in the bulk peat cores range from 3.5 to 12.8 ng cm−2 year−1, which are different in both absolute values and trends from those of nearby sediment cores. Concentrations of PAHs in Sphagnum and Ledum at the surface are similar, indicating the accumulation ability by adsorption and uptake between two species of plants are similar. However, at depths of 5–30 cm, concentrations of PAHs in Sphagnum peat are higher than those in Ledum peat, which can be attributed to their different PAH accumulation abilities or to different PAH degradation rates. An increase in PAHs/TOC ratios with depth in Sphagnum peat indicates that PAHs are resistant to degradation in Sphagnum peat. While a significant positive correlation between C/N and PAHs in Ledum peat suggests that PAHs may be degraded during peat decomposition in Ledum peat. This study finds a difference in PAH concentrations between Sphagnum and Ledum peat. The results suggest that peat quality rather than microbials results in a difference in both PAH accumulation and degradation in peat cores.

First AMS radiocarbon dating of Río Chico style paintings (southernmost Patagonia, Argentina): Older than expected

A 40,000-yr record of environmental change from Burial Lake in Northwest Alaska

The antiquity of Olivella shell beads at CA-ORA-64: AMS radiocarbon dated between 9420 and 7780 cal BP

Modern climate research has shown that the Asian summer monsoon water vapor transport is limited to the eastern part of the Qilian Mountains. On the Holocene millennial-scale, whether the northwest boundary of the summer monsoon varies according to climate change is a key scientific issue. Yanchi Lake is located in the northern Qilian Mountains and the middle of the Hexi Corridor, where the modern climate is less affected by the Asian summer monsoon. It is a key research area for examining the long-term variations of the Asian summer monsoon. Paleoclimatic data, including AMS C-14 dates of pollen concentrates and bulk organic carbon, lithology, grain-size, mineral composition and geochemical proxies were acquired from sediments of Yanchi Lake. The chronological results show that the lower part of the lacustrine section is formed mainly in the Late Glacial and early Holocene period, while the proxies' data indicate the lake expansion is associated with high content of mineral salts. The middle part of this section is formed during the transitional period of the early and middle Holocene. Affected by the reworking effect, the pollen concentrates AMS 14C dates from the middle part of the section are generally older than those from the lower part. Since the mid-Holocene, Yanchi Lake retreated significantly and the deposition rate dropped obviously. The Yanchi Lake record is consistent with the Late Glacial and Holocene lake records in the Qinghai-Tibet Plateau and the climatic records in typical monsoon domain, which indicate the lake expansion and the strong Asian summer monsoon during the Late Glacial and early Holocene. The long-term monsoonal pattern is different from the lake evolution in Central Asia on the Holocene millennial-scale. This study proves the monsoon impacts on the northwestern margin of the summer monsoon, and also proves the fact that the northern boundary of the summer monsoon moves according to millennial-scale climate change.

<p>The content and the profile distribution of the element composition of the 1 meter high peat deposits in flat frost mound bogs are investigated. The botanical composition of peat is described. The results of the botanical composition analysis of peat showed that deposits consist mainly of sphagnum mosses, lichens, shrubs, green mosses, pine wood, as well as pine and birch bark. A good correlation between the degree of peat decomposition and the brightness of dry peat measured by the CIE L*a*b* color model is revealed. As a result of the study of peat samples’ color, it has been found that this parameter can be used as an express method for the rapid assessment of peat degree decomposition. The highest concentration of the organic carbon occurs at the base of the peat deposit (64.4±0.2%). The nitrogen concentration in permafrost peat is higher than in thawed (1.0 ± 0.2% and 0.7 ± 0.1%, respectively, the difference is significant at p = 0.001). The C / N ratio decreases from 72 ± 16 in 0-40 cm in the thawed layer to 50 ± 10 in the frozen part (40-100 cm). Within the bottom low boundary of the seasonally thawed layer, a local increase in the N concentration was detected, as well as an almost 2-fold decrease in the C/N ratio. It is most likely related to the high increase in the rate of microbial activity on the border between the thawed layer and the permafrost peat. It was revealed that most of the elements are concentrated in the upper (thawed) part of the peat deposit. Among them, only Na, Mg, Ca, Zn, Ba, As and Sb have a significant difference. Despite the fact that significant differences according to non-parametric U-criterion Mann-Whitney test were identified only for 7 elements, the distribution of the rest along elements the frozen and thawed peat layer is similar in nature. So for Na, Mg, Al, P, K, Ca, Ti, Fe, Zn, Ba, Li, B, V, Cr, Mn, Co, Ni, Cu, Ga, As, Rb, Sr, Y, Zr, Nb, Mo, Cd, Sb, Cs, the upper quartiles of concentrations in the seasonally thawed layer are 1.2 - 6.9 times higher than in the permafrost peat, and for C, N, Al, Ba, B, V, Co, Cu , Zr, Nb, Mo it is 1,0 - 0,6 times lower, respectively. Generally, according to the element composition, it is safe to say that the differences stem from the botanical composition. In general, according to the elemental composition it can be said that the differences are primarily due to the botanical composition. The active layer comprises mainly sphagnum mosses and lichens, the woody peat already appears in the lower permafrost part of the deposit. A correlation between the brightness of peat and the total content of ash elements (R2 = 0.65, excluding 1 sample) was revealed within the active layer. Taking into account the fact that the brightness correlates with the degree of decomposition, it may be concluded that higher upper quartile of the concentrations of elements in the active layer relates to the slower peat accumulation rate for the last 3 thousand years and, correspondingly, a large accumulation of dust components from the atmosphere by the peat layers.</p>

Peat soils of the taiga zone of West Siberia have historically been relatively poorly studied. In the diagnostics of peat soils, the question of the belonging of the sphagnum litter horizon to the soil profile, as well as the identification of its lower boundary, remains unresolved. In the WRB and Russian Soil Classification, sphagnum litter is considered as a vegetation cover, while in the Soviet classification it is considered as an integral part of the soil profile. The last point of view is also shared by the majority of Russian researchers. Using the material obtained in the study of peat soils in the basin of the river Kazym (subzone of the northern taiga, West Siberia), a comparative characteristic of the sphagnum litter horizon (0–20 cm) and the underlying peat horizon (20–50 cm) was carried out using three parameters: the botanical composition of peat, the degree of peat decomposition, and the color of the soil. All soils are differentiated into the litter horizon and the peat horizon by at least one parameter (5% of the profiles), but in 71% of cases, by three at once. The degree of profile differentiation into two horizons tends to increase in a series of soils formed, respectively, in oligotrophic pine-shrub-sphagnum, oligotrophic complex ridge-hollow, and mesotrophic biogeocenoses. In the overwhelming majority of oligotrophic peat soils, the transition from the litter horizon to the peat horizon is gradual, which does not allow a reproducible assessment of the boundary position in the soil profile. It is proposed to establish a fixed border of the litter horizon at 20 cm from the surface of the bog, referring it to the surface horizon of peat soil.

A review of literature data on the degree of peat decomposition – an important parameter that yields data on environmental conditions during the peat-forming process, i.e., humidity of the mire surface, is presented. A decrease in the rate of peat decomposition indicates a rise of the ground water table. In the case of bogs, which receive exclusively atmospheric (meteoric) water, data on changes in the wetness of past mire surfaces could even be treated as data on past climates. Different factors shaping the process of peat decomposition are also discussed, such as humidity of the substratum and climatic conditions, as well as the chemical composition of peat-forming plants. Methods for the determination of the degree of peat decomposition are also outlined, maintaining the division into field and laboratory analyses. Among the latter are methods based on physical and chemical features of peat and microscopic methods. Comparisons of results obtained by different methods can occasionally be difficult, which may be ascribed to different experience of researchers or the chemically undefined nature of many analyses of humification.

Summary Peatlands are an important component of the global carbon cycle because they comprise huge amounts of terrestrial carbon ( C ). Different conditions during peat formation and secondary peat decomposition affect the quantity and composition of soil organic matter ( SOM ) in peats. There are few comparative studies on the chemical composition of SOM in temperate peatland soil. This study investigates compositional changes of SOM functional groups in peats and corresponding peat‐forming plants by Fourier transform infrared ( FTIR ) spectroscopy. Three plant samples and 29 peat samples were taken from seven temperate peatland sites with different genesis and land‐use intensity. Site‐specific differences, such as genesis of the peat, were found to be reflected in the FTIR spectra. In general, there was more variation in FTIR spectra in samples from fens than in those from bogs and peat‐forming plants. The samples from fens have a smaller C–H absorption band than those from bogs and plants, which reflects greater biochemical activity in the minerotrophic than ombrotrophic environments. In addition to peat genesis, drainage and secondary peat decomposition also affect SOM composition substantially. The larger amounts of aliphatic compounds in undrained peats could be explained by selective preservation caused by anaerobic conditions. With increasing drainage of the sites, there was a decrease in the C–H absorption that was accompanied by a relative increase in C=O absorption. These changes in absorption intensities reflect the enhanced aerobic decomposition and mineralization that accompanies drainage and land‐use intensity. However, the ‘degree of peat decomposition’, a diagnostic tool used in the field, is not reflected by OM composition determined by FTIR spectroscopy. Our results contribute to further understanding of changes in SOM composition during peat formation and processes of secondary decomposition caused by drainage.

Peat decomposition proxies of Alpine bogs along a degradation gradient

Record of environmental change by α-cellulose δ 13C of sphagnum peat at Shennongjia, 4000–1000 aBP

The Swedish Time Scale (STS) is aca.13,300-yr-long varve chronology that has been established for the Swedish east coast from >1000 overlapping clay-varve diagrams. We describe the present state of the STS and illustrate the application of this worldwide unique varve chronology for AMS radiocarbon measurements. The results are compared to other14C-dated calendar-year chronologies: dendrochronology, laminated lake sediments and U/Th. Our data set agrees with the oldest part of the dendrochronological calibration curve, and with AMS14C-dated lake lamination data and U/Th on corals down toca.12 ka calendar years bp. Further back in time, the AMS-dated part of the STS partly compares well with lake lamination chronologies and shows that the difference between14C and calendar years decreases rapidly between 12,600 and 12,800 calendar years bp. Such a development seems to contrast with U/Th measurements on corals. We suggest that the cause for the divergence among three supposed calendar-year chronologies lies in the fact that the data points on the marine14C-U/Th curve are more widely spaced in time than the tightly grouped set of terrestrial AMS14C dates, and thus are not able to reflect short-term changes in atmospheric14C. Therefore, we argue that the use of the pre-Holocene part of the calibration program is premature and inadvisable.